Mold on Leyland Cypresses

I have a row of 15 or so Leyland Cypresses, all approx. 8 years old and maybe 15 feet tall, planted too closely together (10 feet apart). I noticed some grayish mold covering the branches starting from the stem going outside. Some branches have already died.

I will take a sample to our local extension office who told me it's root rot over the phone. This is definitely not root rot. My best guess is that it's some type of mold blight caused by lack of sufficient air circulation, especially since the trees are planted against a privacy fence. Would it make any sense to thin out the branches and cut off everything from the bottom to 6 feet height, the height of the privacy fence? Or should I pull out every other tree to give the remaining ones more space and better ventilation? It seems they will all die if I don't try something. But they may already be doomed anyway.

Sabine


Anne's Response:

There is a Grey Mold (Botrytis cinerea) that causes similar symptoms. Planting plants further apart improves the health of the plants and reducing moisture around the plants helps as well. Plants can be sprayed with a fungicide labeled for Botrytis to slow the progress of the condition. The extension office should be able to give you a better diagnosis when they see the plant. Most root rot symptoms on Leylands are odor and brown foliage.